This invention relates to a positioning system, and particularly to a system for positioning equipment, such as a liquid dispenser, with high precision over at least a two dimensional plane.
Coordinate positioning systems are used to carry instruments along two or three orthogonal axes to desired locations to perform some task, such as liquid dispensing, measuring, or milling. While a number of devices use such a positioning system, the system of the present invention is described for use with a liquid dispensing system that dispenses small quantities of liquid, such as dots of epoxy or an encapsulating liquid, on a printed circuit board.
FIG. 1 is a general representation of a known positioning device 10 for moving a carriage 12 that holds a liquid dispensing device 14 over a workpiece 15. Device 10 has a gantry 16 that is moved with a first motor 18 along a y-axis. Gantry 16 has a horizontal beam 20 along which a second motor 22 moves carriage 12 along an x-axis. Dispensing device 14 is moved along a vertical z-axis with a third motor 24. Movement along any or all of these axes can be accomplished with a lead screw as shown here, with a belt drive, or with a rack and pinion. Note that FIG. 1 is merely a general representation for illustrative purposes, but many other configurations for this general type of positioning device have been used; for example, a vertical beam can be moved along the x-axis, while the vertical beam supports a separate horizontal beam that is movable relative to the vertical beam.
For a given device with a positioning system, the device has a total area that the device takes up (a "footprint"), and a workable area, defined here in the xy-plane, over which the device operates on workpieces 15. To work in this workable area along the x and y axes, the device needs additional space along the x and y axes to accommodate motors and beams, bearings sufficient to hold the carriage firmly, and any other needed components. In a typical system, it is not uncommon along the x-axis for the working area W to be no more than 70% of the total width T of the device (note that FIG. 1 is not to scale). With the increasing expense of manufacturing floor space, particularly in clean room environments, it would be desirable to be able to reduce the amount of space that is needed to operate in a given work area, i.e., to reduce the footprint and thereby increase W/T along at least one axis.